This invention relates generally to methods and apparatus for detecting and measuring radiation in computed tomography (CT) imaging and other imaging systems, and more particularly to high-resolution radiation detector arrays having programmable outputs.
In at least one known single slice CT system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon a one row array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and detector.
In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts that attenuation measurements from a scan into integers called xe2x80x9cCT numbersxe2x80x9d or xe2x80x9cHounsfield unitsxe2x80x9d, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
To reduce the total scan time, a xe2x80x9chelicalxe2x80x9d scan may be performed. To perform a xe2x80x9chelicalxe2x80x9d scan, the patient is moved while the data for the prescribed volume coverage is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed.
In at least one known CT imaging system, a multi-row detector array is used. Each row of the detector (or selected combinations of adjacent rows) can be configured to acquire attenuation measurements of different, parallel imaging planes or xe2x80x9cslicesxe2x80x9d of the object or patient being scanned. However, because of the total number of attenuation measurements that must be processed when a multi-slice scan is performed, a very high bandwidth data path must be provided in multi-slice CT imaging systems. The high-bandwidth data path is a communication path provided between the detector array and an image reconstructor. The communication path includes a data acquisition system (DAS), and is limited by one or more of the number of communication signal lines from the detector array to the DAS, a processing capability of the DAS, and a signal bandwidth (measured, for example, in bytes per second) from the DAS to the image reconstructor. This maximum limit of the communication path is referred to as the maximum bandwidth limit, or maximum data bandwidth.
As a result of bandwidth limitations, multi-slice CT imaging systems are limited in the number of slices of imaging data that can be acquired in a scan. For example, in one imaging system in which a sixteen-row detector array is provided, no more than four slices of attenuation data are acquired during a scan. (When all sixteen detector rows are used, measurements from four adjacent detector rows are inseparably combined for each slice prior to acquisition of the measurements.) Thus, known CT detector arrays have relatively limited resolution, or only a few rows with high resolution. (The smallest detector element in one known system is about 1 mm by 2 mm.)
In one known non-rotating digital radiographic system, images are produced by detector arrays having approximately 100 times the number of detector elements per unit area as in known CT imaging systems. Detector arrays having a similar resolution in a rotating imaging system would provide the capability of scanning various body parts at resolutions best suited for clinical needs. However, the limited bandwidth available for data transmission in rotating imaging systems has prevented the use of high-resolution scanned detector arrays.
It would therefore be desirable to provide scannable, high-resolution detector arrays suitable for use in rotating imaging systems. It would also be desirable to provide CT imaging systems having scannable detector elements that do not require extremely high bandwidth. It would further be desirable to provide methods and apparatus for operating a detector array that can selectively provide a high resolution for rotating imaging systems.
One embodiment of the present invention is therefore a detector array for an imaging system, the detector array having a plurality of electrically conductive busses, a plurality of detector elements arranged in rows extending in an x-direction and columns extending in a z-direction, a plurality of scan lines, each operatively coupled to at least one of the detector elements so that electrical activation of one of the scan lines transfers an electrical charge from the detector element onto one of the busses; a plurality of read-out lines; and an interconnection matrix operatively coupled to the busses and the read-out lines and electrically reconfigurable to transfer electrical charges from the busses selectively to the read-out lines.
This embodiment provides a scannable, high-resolution detector array for a rotating imaging system that does not require extremely high bandwidth, and that can selectively provide high resolution, for example, to particular areas of a patient.